Why is the date of the Spring Festival always uncertain?

The latest lunar month around beginning of spring is called the Spring Festival, because the moon is uncertain on a certain day in the Gregorian calendar every year, so the Spring Festival is also uncertain. The following is a supplement to your relevant calendar knowledge. A year is the time for the earth to go around the sun along the ecliptic, which is almost 365.25 days. The 24 solar terms are determined strictly according to the position of the earth on the ecliptic. Every 15 degree is a solar term. Where the earth moves, that day is the solar term. The Gregorian calendar defines a year as 365 days, and there is a leap day every four years, so 24 solar terms's position in the Gregorian calendar is relatively fixed, but sometimes there is a difference of one or two days, which is entirely due to the leap day in the Gregorian calendar. The Gregorian calendar takes years as the unit, and January is one twelfth of a year. Later, it was ravaged by the rulers and became irregular. February became 28 days, and July and August became a big month. A month in the lunar calendar is a full moon, almost 29.5 days. In addition, the lunar calendar is based on months. Because a year is more than 12 months and less than 13 months, it is often rounded. Some lunar years are 12 months and some are 13 months.